You can’t plug a microphone with a 1/8″ plug into a new Mac Pro. Here’s why.

I’ve got a microphone to review for Macworld, specifically for its use with speech recognition software such as Dragon Dictate. (Amazon.com, Amazon UK) I was surprised to find that the Mac Pro doesn’t recognize this microphone.

“Audio out: The left audio port with a speaker icon is a 1/8″ stereo minijack for audio line out. It can use analog audio and digital S/PDIF fibre optic cables. Audio devices you connect to the port will appear in System Preferences > Sound > Output. Note that this port does not support headsets or microphones.

“Headphone port: The right audio port with a headset icon is a 1/8″ stereo minijack for headphones. When you plug in headphones to this port, sound is redirected from the internal speakers to the headphones. Headphones will appear in System Preferences > Sound > Output. If the headset contains a microphone, it will appear in System Preferences > Sound > Input. iPhone headsets including mic and inline controls are supported. Digital output devices are not supported on this port.”

You’d expect that the headphone port would work with a microphone. When I plug a Sennheiser PX 100 II-i into that port, it shows up in the Input pane of the Sound preferences as External Microphone.

But when I plug the microphone I’m reviewing into the same port, it doesn’t show up. Since it’s a microphone only – not a headset with mike – it’s not recognized.

I’m not sure why this is the case, but I suspect it has something to do with the type of plugs each device has. As you can see in this photo, the Sennheiser headset with microphone has a 4-part plug; the other microphone has a 3-part plug. My guess is that the Mac Pro is recognizing the different parts of the plug in order to detect whether or not it will recognize the device.

Whatever the case, it’s important to know that a standard microphone with a 1/8″ plug won’t work in the Mac Pro. If you have one, and want to use it with the Mac Pro, you’ll need some other way of getting the audio into the computer, such as a USB adapter. (Amazon.com, Amazon UK) The mike I’m testing does come with a USB adapter, but I wanted to try it without the adapter to see if there was any difference in accuracy.